Food allergies are a common health problem in dogs and are not rare in cats. Allergies to dietary ingredients can cause dermatological (skin and ear) or gastrointestinal issues. Common skin-related symptoms include redness and itchiness of the paws, ear infections, and anal gland inflammation (causing licking or scooting). Rashes, itchiness, dry skin, and hair loss can also occur in other parts of the body. Signs of gastrointestinal upset such as loose stool or diarrhea, excessively frequent or large bowel movements, thin body condition, and vomiting can also occur with a food allergy. When both gastrointestinal and dermatological signs are present, we are very suspicious of diet-related causes. Symptoms that occur year-round rather than seasonally are also suspicious for an underlying food allergy.
There is a common misconception that grains are the main culprit behind food allergies in dogs and cats, perpetuated in the last several years by the marketing teams of pet food companies. In reality, evidence shows that dietary protein sources are commonly implicated in causing allergies. Common allergic triggers include chicken, beef, dairy, and soy, as well as corn and wheat.
Unfortunately, there is no lab test that can diagnose food allergies in your pet. Blood tests for food allergies are inaccurate and a waste of money. A limited ingredient diet trial is the only way to reach a diagnosis and discover what ingredients cause symptoms. When your veterinarian is suspicious of a food allergy, they will recommend a prescription diet trial for at least eight weeks. Trials need to be conducted with a limited ingredient diet to have the greatest chance of success and to reduce confusion about what ingredients are triggering clinical signs.
It is important that we choose a diet containing a protein source and a carbohydrate source that your pet has never previously ingested, and therefore has never had the opportunity to become sensitized to. Often, we choose unusual proteins such as venison or kangaroo, along with potato, green pea, or oatmeal. Alternatively, we may recommend a hydrolyzed diet, especially for dogs with gastrointestinal signs. Hydrolyzed diets are composed of a protein such as chicken or soy that has been enzymatically broken down so that it is less likely to trigger the immune system. Pet store diets are not recommended for feeding trials. Studies have shown many over the counter limited ingredient diets contain traces of other protein sources, so they may trigger allergy symptoms and cannot accurately diagnose a food allergy.
The feeding trial needs to be strict for at least eight weeks, with no treats, chews, bones, flavoured medications (including parasite prevention), fruits, or vegetables fed during the initial period. We should see some improvement in gastrointestinal symptoms in about two weeks, whereas skin issues can take 4 to 8 weeks to see a change.
After the initial trial period is over, you can speak to your veterinarian about doing dietary challenges to determine what your pet is sensitive to. Anything used to challenge should be a single ingredient (i.e. cooked chicken), and this ingredient should be introduced for at least two weeks before adding another. Any clinical signs that occur should be reported to your veterinarian.
Written by: Dr. Megan Edwards, DVM
